This proposal pursues the possibility that mediators of cell injury not only cause cell death but also induce heat shock and regulatory genes that promote repair and improve survival of injured neurons. Ischemia, excitotoxins, and prolonged seizures induce heat shock proteins (HSPs) in brain. This project will determine whether the neurons and glia that express HSP72 protein have electron microscopic evidence of membrane or organelle injury. Following global ischemia, focal ischemia and following administration of kainic acid, brain cells stained immunocytochemically for HSP72 will be examined under the electron microscope for evidence of injury. Cultured neurons will also be injured by increasing concentrations of excitotoxins or ischemia. Cell injury, total protein synthesis, and hsp72 mRNA and HSP72 protein expression are evaluated day later. It is proposed that induction of HSPs will be associated with cell injury, that maximal HSP72 expression will correlated with good cell survival, and that as injury increases protein synthetic machinery will be damaged resulting in failure of HSP72 and total protein synthesis in cells that will die. The predictions will also be tested in adult rats and sustain global ischemia. One to three days after the ischemia total protein synthesis in individual neurons will be measured in single cells following 3H leucine administration and compared to induction of HSP72 protein and hsp72 mRNA in the same cells. Since prior induction of HSPs protects many cell types including retinal neurons from injury, we will determine whether prior induction of HSPs, as indicated by HSP72, protects central neurons in vitro and in vivo. HSP72 will be induced in cultured neurons, and the survival of these cells following hypoxia/hypoglycemia and following administration of excitotoxins will be compared to controls. HSP72 will also be induced in vivo using several methods. Subjects are then made globally ischemic at different times after HSP induction and neuronal cell survival compared to controls. It is predicted that cerebral protection will correlate with maximal HSP induction. Possible mechanisms of HSP72 induction will also be examined in cultured neurons by altering medium concentrations of calcium, glucose, and hydrogen ions; and by testing whether NMDA receptor blockers and calcium channel blockers prevent HSP72 induction by hypoxia/ischemia in vitro.